The microbial colonization of elemental sulphur in sewage sludge was studied by scanning electron microscopy (SEM). The indigenous sulphur-oxidizing microflora grown at the sulphur surface produces a filamentous matrix between the cells and the substrate. This material, similar to bacterial glycocalyx, confers to this biomass an ecological advantage allowing dense colonization. These adhesion structures were also observed with Thiobacillus thiooxidans ATCC 55128 growing in sewage sludge and in a synthetic mineral medium with Thiobacillus thiooxidans ATCC 19377 and Thiobacillus intermedius ATCC 15466 in synthetic medium. The production of this filamentous material was not observed with Thiobacillus thioparus ATCC 55127 cultured in sludge or in synthetic medium. The observation of these connections between cells and sulphur and among cells with the three acidophilic strains tested and with sulphur-oxidizing microflora indicate that this adhesion mechanism could play a significant role in sulphur colonization and oxidation in the natural environment.